Automatically Authenticating a User

Hi, We have a requirement to authenticate a user directly to the web page without giving username and password when accessed through our public portal. The application license does not allow guest/annonymous user. It supports only named users. How can we allow the user directly to the site using F5 as a proxy in between? Is there a solution using APM or iRules. Appreciate if you could show a sample script.

 

Thanks